Day_ fifteen

1. BigInteger

1.1 summary

Integer Class as int The wrapper class , The maximum integer value that can be stored is 231-1,Long Classes are also finite , The maximum is 263-1. If you want to represent a larger integer , Whether it's basic data types or their wrapper classes There's nothing we can do , Not to mention doing calculations

java.math Bag BigInteger Can represent immutable integers of any precision .BigInteger Provide

all Java The equivalent of the basic integer operator of , And provide java.lang.Math All the relevant methods . in addition ,BigInteger The following operations are also provided ： Modular arithmetic 、GCD Calculation 、 Prime number test 、 Prime generation 、 Bit operations and some other operations

1.2 Use

Add and + .add

  Subtracting the -        .subtract

  The product of *        .multiply

  except /        .divide

  Remainder %        .remainder

2. Math

 2.1 summary

java.lang.Math A series of static methods are provided for scientific calculation . The parameters and returns of its method

The value type is generally double type

2.2 Common methods

3. Exception mechanism

3.1 Common abnormal

① Null pointer exception

② Subscript out of range exception

③ Type conversion exception

④ Stack memory overflow

3.2 summary

Exception is Java Provides a consistency mechanism for identifying and responding to error conditions . Effective exception handling can make the program more robust 、 Easy to debug , It's a saying that goes wrong

3.3 Abnormal reason

①   The user entered illegal data

②  The file to be opened does not exist

③ The connection is broken during network communication

④ JVM out of memory

⑤  Some of these exceptions are caused by user errors , Some are caused by program errors , Others are caused by physical errors

3.4 Inheritance system

 3.5 Exception

summary :

Exception Is the parent of all exception classes . Divided into non RuntimeException and RuntimeException

Not RuntimeException It refers to the exceptions that need to be caught or handled during program compilation

RuntimeException It refers to the exception that does not need to be caught or handled during program compilation

Common methods :

 3.6 try...catch...

try...catch... : Handling exceptions , Generally used for client

Statement :

 

3.7 throws

throws Throw an exception , This approach does not deal with solving problems , Is a reminder mechanism , Tell the caller , There may be errors here

If guidance on how to solve , Then use try solve the problem , Otherwise, it will pass throws Ask questions as long as the next family reminds you , Either you solve the problem , Otherwise, it will pass throws Throw questions

throws Multiple exceptions can be thrown at the same time , Multiple are separated by commas

3.8  finally

finally : Statement blocks that must be executed , Not to be used alone , It has to be with try perhaps try..catch.. Use it together

 finally There is only one case of non execution , That's it System.exit(0);

Statement :

3.9  There can be no broader exceptions

Method override , You cannot have a broader exception than the original method

Exceptions thrown by subclass methods , Cannot be greater than the parent exception , That is, exceptions less than or equal to the parent class can be

 4. Custom exception classes

1. Inherit an existing exception class , If it's a runtime exception , Then inherit RuntimeException Otherwise, it inherits Exception Generally speaking , We wrote It must be a compile time exception

2. Public parameterless construction

3. Public parameterized constructs , Parameters are error messages , And then through super Pass it to the parent class